Field of the Invention
The present invention relates to a display device integrated with touch screen, and more particularly, to a display device integrated with touch screen and a driving method thereof, which can reduce a parasitic capacitance to enhance touch sensing performance.
Discussion of the Related Art
Display devices often include touch screens instead of a mouse or a keyboard to enable a user to directly input information with a finger or a pen that is applied to one of the flat panel display devices.
Touch screen are used in monitors such as navigations, industrial terminals, notebook computers, financial automation equipment, game machines, portable terminals such as portable phones, MP3 players, PDAs, PMPs, PSPs, portable game machines, DMB receivers, tablet personal computers (PCs), and home appliances such as refrigerators, microwave ovens, and washing machines.
A touch screen can be an in-cell type in which the touch screen is built in a cell of a display panel, an on-cell type in which the touch screen is disposed on a display panel, and an add-on type in which the touch screen is separately coupled to an upper portion of a display device, according to a structure. The in-cell type touch screen has an aesthetic design and is slim, and thus is becoming more prevalent.
FIG. 1 is a diagram schematically illustrating a related art display device integrated with a touch screen.
The related art display device integrated with the touch screen includes a display panel. The display device can also include a gate driver, a data driver, and a touch driver.
A plurality of pixels are formed in the display panel, and the touch screen is configured with a plurality of touch electrodes 10. In this case, the touch electrodes 10 and the pixels are formed in the display panel. A common electrode, which is formed for supplying a common voltage (Vcom) to each of the pixels, is used as the touch electrode 10.
Here, the plurality of touch electrodes 10 is divided into a plurality of driving electrodes (TX) 12, which receives a touch driving signal, and a plurality of receiving electrodes (RX) 14 that sense a touch. Each of the plurality of receiving electrodes 14 is formed in a one-piece line shape so as to have a bar shape from an upper portion to a lower portion of the display panel. The plurality of driving electrodes 12 are formed in units of a certain number of pixels.
A plurality of driving electrode lines 20, which supply a touch driving signal to the plurality of driving electrodes 12, are formed in the display panel. A plurality of driving electrodes 12, which are formed on the same horizontal line, are connected to each other by a corresponding driving electrode line 20. A plurality of receiving electrode lines 30, which sense capacitances of the plurality of receiving electrodes 14, are formed.
The touch driver is configured with a touch driving integrated circuit (IC) and a touch sensing IC. The touch driving IC is connected to the plurality of driving electrode lines 20, and supplies the touch driving signal to the plurality of driving electrodes 12. The touch sensing IC is connected to the plurality of receiving electrode lines 30, and senses a touch signal.
FIG. 2 is a diagram illustrating a method of driving the related art display device integrated with touch screen.
The display panel 10 which is integrated with the touch screen in an in-cell touch type temporally divides and drives a display operation and a touch sensing operation due to a structural characteristic in which the common electrode for display is used as the touch electrode.
The display operation may be performed in a partial period of one frame period by time-division driving the display panel in units of a frame, and the touch sensing operation may be performed in the other non-display period.
The display operation may be performed, in a partial period of one horizontal period (1H) by time-division driving the display panel in units of a line, and the touch sensing operation may be performed in the other non-display period.
In a display period, the display panel supplies data voltages based on image data and the common voltage to all the pixels to display an image. In a touch sensing period, the display panel supplies the touch driving signal to the plurality of driving electrodes TX1 to TXn, and senses touch signals of the plurality of receiving electrodes RX1 to RXn. A capacitance deviation occurs between a touched touch electrode and an untouched touch electrode, and the touch sensing IC senses the capacitance deviation between the touch electrodes to detect whether there is a touch and a touched position.
In the related art in-cell touch type display device, for the common electrode of the display panel to be used as the touch electrode 10, the plurality of driving electrode lines 20 and the plurality of receiving electrode lines 30 are formed to intersect each other, and thus, a parasitic capacitance “Cp” of the touch electrode 10 increases.
                    Cp        =                  ɛ          ⁢                      A            d                                              [                  Equation          ⁢                                          ⁢          1                ]            
where Cp denotes a parasitic capacitance, ε denotes a permittivity of the touch electrode, A denotes a cross-sectional area of the touch electrode, and d denotes a distance between the touch electrodes. The parasitic capacitance “Cp” is inversely proportional to the distance “d” between the touch electrodes, and increases in proportion to the cross-sectional area “A” of the touch electrode.
In the in-cell touch type, since the driving electrode 12 and the receiving electrode 14 are formed on the same plane, a distance between electrodes is short, and since the plurality of driving electrode lines 20 and the plurality of receiving electrode lines 30 are formed in a cell, the parasitic capacitance “Cp” increases. As a screen size of the display panel increases, the parasitic capacitance “Cp” increases exponentially, and when the parasitic capacitance “Cp” increases, a sensing performance of the touch IC decreases. The decreased sensing performance of the touch IC can be caused by enlarged sizes of the in-cell touch type display device.